EP4341708A1

EP4341708A1 - Method and control device for determining an energy quantity in a battery or battery cell

Info

Publication number: EP4341708A1
Application number: EP22712575.4A
Authority: EP
Inventors: Marian VLCEK; Jiri VALTR; Adam Hrazdira; Stefan Aust
Original assignee: Volkswagen AG
Current assignee: Volkswagen AG
Priority date: 2021-05-20
Filing date: 2022-03-10
Publication date: 2024-03-27
Also published as: DE102021205163A1; WO2022242926A1; CN117355758A

Abstract

The invention relates to a method for determining an energy quantity (20) in a battery or battery cell, wherein: an initial charge state (10) is received; a final charge state (11) is received; a load profile (12) between the initial charge state (10) and the final charge state (11) is received; intermediate charge states (14) between the initial charge state (10) and the final charge state (11) and associated weighting factors (15) are determined; parameters (16) of an equivalent circuit model (30) of the battery or the battery cell are estimated for each of the determined intermediate charge states (14); and, proceeding from the load profile (12), the weighting factors (15) and the parameters (16), an energy quantity (20) of the battery or battery cell between the initial charge state (10) and the final charge state (11) is determined and is provided as an energy quantity signal (21). The invention further relates to a control device (1) for determining an energy quantity (20) in a battery or battery cell.

Description

description

Method and control device for determining an amount of energy in a battery or

battery cell

The invention relates to a method and a control unit for determining an amount of energy in a battery or battery cell.

Due to increasing electrification of vehicles, batteries, especially lithium batteries, are becoming more and more important. An important parameter is an amount of energy that is taken from or added to the battery when it is in operation. A remaining range, an operating time or an amount of energy required to fully charge the battery can be determined with the aid of energy quantities. A quantity of energy can be determined both in the charging direction and in the discharging direction. In addition, an amount of energy can also be determined in intervals between states of charge (SOC) of the battery. Determining amounts of energy accurately is crucial for determining a (current) state of the battery.

A recursive method for adaptive multi-parameter regression is known from US Pat. No. 7,612,532 B2, which is expanded by forgetting factors that are unique for each regressive parameter. Applications of this process can include lead-acid batteries, nickel-metal hydride batteries, and lithium-ion batteries, among others. A control method is presented that has an arbitrary number of model parameters, each with its own time weighting factor. A method for determining optimal values for the time weighting factors is included to give more effect to recently obtained system state determination data. A weighted recursive least squares method is used, with time weighting conforming to the exponential forgetting formalism. The derived result does not involve any matrix inversion and the procedure is iterative, ie each parameter is fed back individually at each time step. The invention is based on the object of creating a method and a control device for determining an amount of energy in a battery or battery cell, in which the amount of energy can be reliably determined.

The object is achieved according to the invention by a method having the features of patent claim 1 and a control unit having the features of patent claim 6 . Advantageous configurations of the invention result from the dependent claims.

In particular, a method for determining an amount of energy in a battery or battery cell is provided, with a starting charge state being received, with a discharging state being received, with a load profile between the starting charge state and the discharging state being received, with intermediate charging states between the starting charge state and the discharging state and associated weighting factors are determined, with parameters of an equivalent circuit model of the battery or battery cell being estimated for each of the intermediate charge states determined, and with an amount of energy in the battery or battery cell between the starting charge state and the discharge state being determined on the basis of the load profile, the weighting factors and the parameters, and as an energy quantity signal provided.

Furthermore, in particular a control unit for determining an amount of energy in a battery or battery cell is created, the control unit being set up to receive an initial charge state, to receive an end charge state, to receive a load profile between the initial charge state and the end charge state, to receive intermediate charge states between the initial charge state and the To determine the final state of charge and associated weighting factors, to estimate parameters of an equivalent circuit model of the battery or battery cell for each of the intermediate states of charge determined, and to determine an amount of energy in the battery or battery cell between the initial state of charge and the final state of charge on the basis of the load profile, the weighting factors and the parameters and as provide energy quantity signal.

The method and the control unit make it possible to determine, in particular to estimate, an amount of energy in an improved manner. For this purpose, it is provided that parameters of an equivalent circuit model of the battery or the battery cell are estimated for intermediate charging states that lie within an interval between a starting charging state and an end charging state. In this case, the parameters are estimated, in particular, as a function of the intermediate charge state considered in each case. Furthermore, in particular, a temperature or a temperature dependency is taken into account when estimating the parameters. The parameters are therefore dependent in particular on the respective intermediate charging state and the prevailing temperature. The temperature can be detected, for example, by means of a temperature sensor on the battery or battery cell, or it can be provided in some other way, for example, it can be estimated. Based on a received load profile, the weighting factors and the estimated parameters, the amount of energy in the battery or battery cell between the starting charge state and the end charge state is determined. The determined amount of energy is provided as an energy amount signal. The energy quantity signal can be analog or digital. The energy quantity signal can be transmitted to a battery controller and/or a vehicle controller or a charging infrastructure, for example.

One advantage of the method and the control unit is that losses occurring in the battery or battery cell can be taken into account in an improved manner by taking into account state-of-charge-dependent and, in particular, also temperature-dependent parameters. The amount of energy between the initial charging state and the final charging state can therefore be determined in an improved manner.

The starting state of charge and the discharge state are in particular between a minimum state of charge and a maximum state of charge of the battery or battery cell. The starting state of charge and the discharged state of charge are received, for example, as an analog or digital signal from the initial state of charge and as an analog or digital signal from the discharged state of charge, for example from a battery controller and/or a vehicle controller. The starting state of charge and the discharge state can also be queried from a battery controller or a vehicle controller.

A load profile refers in particular to a current during charging and/or during discharging between the initial charging state and the final charging state. The load profile can be based on recorded sensor data (current measurement) as well as on specified, e.g. simulated or estimated data. In particular, the load profile can be time-resolved.

The parameters of the equivalent circuit model can, for example, have been determined empirically for different states of charge and temperatures of the battery. The parameters determined are then stored in a memory, in particular in the control unit, and can be called up as required and, if necessary, made available in an interpolated form if the parameters are to be estimated for an intermediate charging state. It is however, alternatively or additionally, it is also possible to determine and/or estimate the parameters by simulation.

The determined intermediate charge states form, in particular, interpolation points in a numerical integration carried out to determine the amount of energy. In particular, provision is made for the intermediate charging states between the starting charging state and the final charging state and the associated weighting factors to be determined as a default by a selected numerical integration method. In other words: the selected numerical integration method specifies the intermediate charge states and the associated weighting factors as support points. In this way, an amount of energy can be determined within any desired state of charge interval by integration over a voltage of the battery or battery cell. For example, open or closed Newton-Cotes formulas can be selected as numerical integration methods, in which uniformly distributed interpolation points are used. Support points that are not uniformly distributed can also be used by means of Gauss-Legendre squaring. The methods differ in the choice of support points, but the rest of the procedure is the same. In particular, the integral is always calculated as the weighted sum of the stresses at the interpolation points. In principle, however, other numerical integration methods can also be used.

Parts of the control device can be designed individually or combined as a combination of hardware and software, for example as program code that is executed on a microcontroller or microprocessor. However, it can also be provided that parts are designed individually or combined as an application-specific integrated circuit (ASIC) or field-programmable gate array (FPGA).

The method and the control device can be used in particular in a vehicle, in particular a motor vehicle. In principle, however, a vehicle can also be another land, rail, water, air or space vehicle, for example a drone or an air taxi. In principle, however, the method and the control unit can also be used in other mobile or stationary energy stores.

In general, an amount of energy can be calculated as follows: Here, Q _N0 mmai is a capacity of the battery or battery cell with the unit Ah (ampere hours), SOC _start is the starting charge level, SOC _End is the final charge level (each without a unit as a percentage or value between 0 and 1), U is the voltage of the battery or Battery cell and SOC the state of charge of the battery or battery cell.

The integral is solved using a numerical integration method, for example using one of the open or closed Newton-Cotes formulas:

In this case, w _t is the weighting factor at the interpolation point i corresponding to an intermediate charge state SOC _t .

In one embodiment, it is provided that the equivalent circuit model includes at least one open-circuit voltage as a voltage source, a series resistance and at least one RC element. As a result, the essential effects in the battery or battery cell can be taken into account; in particular, a time-dependent behavior can be taken into account by means of the at least one RC element. In particular, the equivalent circuit model has more than one RC element, so that multiple time-dependent processes within the battery or battery cell can also be taken into account.

In one embodiment it is provided that, in order to determine the amount of energy for each intermediate charging state, a total voltage of the battery or battery cell is determined at least from the open-circuit voltage, a series resistance voltage drop across the series resistance and an RC element voltage drop across the at least one RC element. This enables the amount of energy to be determined particularly efficiently. In particular, the RC elements are connected in series.

The voltage of the battery or battery cell is then given as: Here, U _ocv is the open-circuit voltage, U _R0 is the series resistance voltage and U _{RC n} is the RC element voltage dropping across the nth RC element. This applies to each intermediate charge state SO :

The no-load voltage t/ _ocv is estimated as a parameter by the equivalent circuit model as a function of the intermediate charge state SO.

It then results for the amount of energy E\

In a further embodiment, it is provided that the load profile is received in the form of a root mean square value of a current and a mean value of the current, with the series resistance voltage dropping across the series resistance being determined from the root mean square of the current and the mean value of the current for the intermediate charging states. This allows the series resistance voltage to be reliably determined, particularly in the case of load profiles with a non-constant current curve.

The series resistance voltage URO-, which is dependent on the intermediate charge state SO, is obtained

Here, R ₀ is the series resistance dependent on the intermediate charging state SO, I _RMS is the root mean square of the current and I _Avg is the mean value of the current. R ₀ is a parameter that is estimated using the equivalent circuit model for the respective intermediate charge state. The average values can also be average values over a few interpolation points around the interpolation point under consideration (for example in the form of a moving average that takes into account a predetermined number of interpolation points). In a further developing embodiment it is provided that to determine the RC element voltage dropping across the at least one RC element, starting from the initial charge state, a time is determined until reaching the intermediate charge state considered in each case, with the RC element voltage starting from the certain time and a time constant of the at least one RC element is determined. As a result, the RC element voltage of the at least one RC element can be estimated in an improved manner and the total voltage can subsequently also be determined in an improved manner.

For the time t _j to reach the intermediate state SO considered, the following results:

The RC element voltage U _{RC n} that depends on the intermediate charge state SO then results in:

Here t _h is the time constant for the nth RC element. The RC element resistance R _{ßC n} is estimated as a parameter depending on the intermediate charge state SO using the equivalent circuit model.

In order to reduce the computing power required, it can also be assumed in one embodiment that the RC elements are saturated so that they can be replaced by constant resistors. Such a procedure is possible in particular with a constant load (constant current in the load profile) and/or large intervals between the initial charge state and the end charge state.

Additional features relating to the configuration of the control unit result from the description of configurations of the method. The advantages of the control device are the same in each case here as in the case of the refinements of the method.

The invention is explained in more detail below on the basis of preferred exemplary embodiments with reference to the figures. Here show: 1 shows a schematic representation of an embodiment of the control device for determining an amount of energy in a battery or battery cell;

FIG. 2 shows a schematic flow chart of processing in the control unit according to an embodiment of the method; FIG.

3 shows a schematic representation of an equivalent circuit model.

1 shows a schematic representation of an embodiment of control unit 1 for determining an amount of energy 20 in a battery or battery cell.

The control device 1 comprises a computing device 2 and a memory 3. The computing device 2 is, for example, a microprocessor or a microcontroller on which program code is executed in order to carry out the method described in this disclosure. However, hard-wired hardware components can also be provided, which partially or fully execute the method. Control unit 1 can be part of a battery control system.

An initial charge state 10, an end charge state 11 and a load profile 12 are supplied to control unit 1. Provision can also be made for a current temperature 13 of the battery or battery cell to be fed to control unit 1 . The current temperature of the battery or battery cell can be detected and/or estimated using a temperature sensor 50, for example. The control unit 1 can also form a common device together with the temperature sensor 50 . The starting state of charge 10, the final state of charge 11 and the load profile 12 are queried and/or provided, for example, by an energy management system (not shown) or a vehicle controller 51 of a vehicle (not shown). The starting charge state 10, the end charge state 11 and the load profile 12 are received by the control unit 1 and processed by the computing device 2.

Processing in control unit 1 according to one embodiment of the method is shown schematically as a flowchart in FIG. 2, which illustrates a signal flow. Control unit 1 is set up to determine intermediate charging states 14 between starting charging state 11 and final charging state 12 and associated weighting factors 15 . This takes place in a module 100. For each of the intermediate charging states 14 determined, the control unit 1 estimates parameters 16 of an equivalent circuit model of the battery or the battery cell in a module 101. This also happens in particular taking into account the temperature 13. The estimation is carried out, for example, on the basis of empirically determined parameters of the equivalent circuit model. Provision can be made here for empirically determined parameters to be interpolated. Alternatively or additionally, provision can also be made for the parameters to be estimated on the basis of a simulation.

An exemplary equivalent circuit model 30 is shown schematically in FIG. 3 . It is provided in the example that the equivalent circuit model 30 comprises at least one open-circuit voltage U _ocv modeled in the form of a capacitance C as a voltage source, a series resistance R ₀ and two RC elements RC1, RC2 with the resistances R1, R2 and the capacitances C1, C2 . In principle, however, the equivalent circuit model 30 can also have more or fewer RC elements RC1, RC2.

Parameters 16 (Fig. 2), depending on a respective intermediate charging state 14, are in particular open-circuit voltage U _ocv (Fig. 3), series resistance R ₀ (Fig. 3), a resistance R1, R2 of RC elements RC1, RC2 (Fig 3) and estimated time constants of the RC elements RC1, RC2. Furthermore, a voltage across the RC elements RC1, RC2 for the starting state of charge 10 is also estimated.

Based on the load profile 12 (Fig. 2), which is provided in particular as a mean value 12-1 of the current and as a root mean square 12-2 of the current, the weighting factors 15 and the parameters 16, an amount of energy 20 of the battery or in a module 102 Battery cell between the starting state of charge 10 and the discharge state 11 determined. The determined amount of energy 20 is provided as an energy amount signal 21 .

In order to determine the amount of energy, provision is made in particular for a total voltage U (Fig. 3) of the battery or battery cell for each intermediate charging state 14 to be determined from at least the open-circuit voltage U _ocv , a series resistance voltage U _R0 dropping across the series resistor R ₀ and a series resistance voltage U R0 across the RC elements RC1 , RC2 falling RC element voltage U _RC1 , U _RC2 is determined.

It is provided in particular that for the intermediate charging states 14 the series resistance voltage U _R0 dropping across the series resistor R ₀ is determined from the root mean square 12-2 (FIG. 2) of the current and the mean value 12-1 (FIG. 2) of the current . Furthermore, in order to determine the RC element voltage U _RC1 , U _RC2 dropping across the at least one RC element RC1, RC2 (Fig. 3), starting from the initial charge state 10, a time is determined until the intermediate charge state 14 under consideration is reached is, wherein the RC element voltage U _RC1 , U _RC2 is determined based on the specific time and a time constant of the at least one RC element RC1, RC2.

The resulting total voltage U of the battery or battery cell is then integrated numerically over the interval between the initial charging state 10 and the final charging state 11 in order to obtain the amount of energy 20 . This can be done, for example, using open or closed Newton-Cotes formulas. In principle, however, other numerical integration methods can also be used. From the energy quantity 20 obtained, the energy quantity signal 21 is then generated, which encodes the value of the energy quantity 20 in a suitable form. The energy amount signal 21 can be fed to a battery controller 52 or the vehicle controller 51, for example.

In particular, the method and the control unit enable an improved determination of amounts of energy in batteries or battery cells. The method and the control unit can advantageously be used in particular at different temperatures and state of charge intervals of different sizes. Furthermore, non-constant load profiles can also be taken into account, so that losses that occur can be better taken into account. Different charging histories can also be taken into account, since the current state of charge of the battery is always taken into account.

Reference List

1 control unit

2 computing device

3 storage

10 Boot State of Charge

11 Discharge state

12 load profile

12-1 Average Current

12-2 root mean square current

13 temperature

14 intermediate charging state

15 weighting factor

16 parameters 20 amount of energy 21 amount of energy signal 30 equivalent circuit model

50 temperature sensor

51 vehicle control

52 Battery Control

100-102 modules

Cx capacity

C capacitance (open circuit voltage)

RCx RC circuit

Rx resistance

U total voltage

Uocv no-load voltage

R ₀ series resistance

URO series resistance voltage

URCX RC link voltage

Claims

patent claims

1. A method for determining an amount of energy (20) in a battery or battery cell, wherein a starting state of charge (10) is received, wherein a discharging state (11) is received, wherein a load profile (12) between the starting state of charge (10) and the

Discharge state (11) is received, with intermediate charge states (14) between the starting charge state (10) and the final charge state (11) and associated weighting factors (15) being determined, with parameters (16) of an equivalent circuit model (30 ) of the battery or battery cell are estimated, and based on the load profile (12), the weighting factors (15) and the parameters (16), an amount of energy (20) of the battery or battery cell between the initial charge state (10) and the end charge state (11 ) is determined and provided as an energy quantity signal (21).

2. The method as claimed in claim 1, characterized in that the equivalent circuit model (30) comprises at least one open-circuit voltage (U _ocv ) as a voltage source, a series resistance (R0) and at least one RC element (RCx).

3. The method according to claim 2, characterized in that to determine the amount of energy (20) for each intermediate charge state (14), a total voltage (U) of the battery or battery cell at least from the no-load voltage (U _ocv ), a voltage drop across the series resistance (R0). Series resistance voltage (U _R0 ) and at least one RC element (RCx) dropping RC element voltage (U _RCx ) is determined.

4. The method according to any one of claims 2 or 3, characterized in that the load profile (12) in the form of a root mean square value (12-2) of a current and a mean value (12-1) of the current is received, for the intermediate charging states ( 14) the series resistance voltage (U _R0 ) dropping across the series resistance (R0) is determined from the root mean square (12-2) of the current and the mean value (12-1) of the current.

5. The method according to claim 3 or 4, characterized in that to determine the at least one RC element (RCx) dropping RC element voltage (U _RCx ) starting from the starting state of charge (10) a time until reaching the respective considered intermediate charge state (14) is determined, the RC element voltage (U _RCx ) based on the determined time and a time constant of the at least one RC element (RCx) is determined.

6. Control unit (1) for determining an amount of energy (20) in a battery or battery cell, the control unit (1) being set up to receive a starting charge state (10), a discharge state (11), a load profile (12) to receive between the start charge state (10) and the end charge state (11),

to determine intermediate charging states (14) between the starting charging state (10) and the final charging state (11) and associated weighting factors (15), to estimate parameters (16) of an equivalent circuit model (30) of the battery or the battery cell for each of the determined intermediate charging states (14), and based on the load profile (12), the weighting factors (15) and the parameters (16) to determine an amount of energy (20) of the battery or battery cell between the initial charge state (10) and the end charge state (11) and to provide it as an energy quantity signal (21). .

7. Control unit (1) according to claim 6, characterized in that the equivalent circuit model (30) comprises at least one open-circuit voltage (U _ocv ) as a voltage source, a series resistance (R0) and at least one RC element (RCx).

8. Control unit (1) according to claim 7, characterized in that the control unit (1) is also set up to determine the amount of energy (20) for each intermediate charge state (14) a total voltage (U) of the battery or battery cell at least from the open circuit voltage ( U _ocv ), a series resistance voltage ( U R0 ) dropping across the series resistance ( _R0 ) and an RC element voltage ( U _RCx ) dropping across the at least one RC element (RCx).

9. Control unit (1) according to any one of claims 7 or 8, characterized in that the control unit (1) is further adapted to the load profile (12) in the form of a square mean value (12-2) of a current and a mean value (12-1) of the current, and for the intermediate charging states (14) the series resistance voltage (U _R0 ) dropping at the series resistor (R0) from the square mean value (12- 2) of the current and the mean value (12-1) of the current.

10. Control unit (1) according to claim 8 or 9, characterized in that the

The control device (1) is also set up to determine the RC element voltage (U _RCx ) dropping across the at least one RC element (RCx), starting from the initial charge state (10), a time until the intermediate charge state (14 ) and to determine the RC element voltage (U _RCx ) based on the determined time and a time constant of the at least one RC element (RCx).